This invention relates to a catalyst, to a method of preparing a catalyst and in particular to a method of preparing a microencapsulated catalyst.
Catalysts, such as transition metal catalysts, are widely used in a variety of chemical reactions. Difficulties are frequently encountered however, particularly on the commercial scale, in recovering and re-using the catalyst. This not only results in potential contamination of the product but also represents a significant cost burden in terms of usage of expensive catalyst. Polymer-supported catalysts are well known but suffer from a number of disadvantages such as poor physical stability and low catalyst availability. Furthermore heterogeneous reaction systems used with polymer-supported catalysts are inherently more complex to operate on a commercial scale.
Various attempts have been made to overcome these difficulties. In EP 0940170 for example there is described a process wherein an aromatic substituted polyolefin such as polystyrene is dissolved in an organic solvent such as cyclohexane to which is added osmium tetroxide catalyst. The solution is cooled and the aromatic substituted polyolefin is precipitated, for example by the addition of methanol. The resultant product was shown to be an effective catalyst. The precipitation of the aromatic polymer however is uncontrolled and results in an amorphous and unstructured mass, monolith or matrix of solid polyolefin within which the osmium tetroxide particles are trapped. It is a further drawback of this process that the trapped catalyst system cannot subsequently be used effectively in a reaction medium in which the polymer is soluble or becomes plasticised since the free catalyst will be liberated. This therefore limits the utility of the catalyst.